U.S. Pat. No. 4,528,790 discloses a roof/ceiling insulation system wherein insulation supporting tubes are suspended from and extend parallel to the purlins or auxiliary support beams, and faced fibrous insulation batts are strung over the tubes perpendicularly to the purlins in each bay defined by a pair of adjacent main support beams. This system requires a tedious special operation for insulating over the main support beam between each bay. A vapor barrier, preferably a plastic film, has to be strung over each section of a main support beam between two adjacent purlins, and then stapled to the facing of the adjacent faced insulation batts strung over the tubes on opposite sides of the main support beam, as shown in FIG. 6 of U.S. Pat. No. 4,391,075. Insulation then has to be placed on top of the plastic film running over the main support beam. Further, many items such as lights, rods, pipes, support hooks, etc. are often hung from the purlins. Whenever these items don't happen to be located between insulation strips, the faced insulation has to be cut.